breakers with multi wire branch circuit (shared neutral)

Hello all.

First off I'll say that I'm in Alberta (for anyone that might comment on code-related issues with my question!).

I'm planning to install a dusk-to-dawn yard light on a 20' pole, with 2 GFCI receptacles (used for 1500W water trough heaters) mounted near the base of the pole. The length of the wire run is about 130' from panel to the pole.

To cut down on wire, I'm planning to use a 12/2 wire for one of the GFCIs (on a stand-alone 20amp breaker, the only thing on the circuit), and a 12/3 wire for the combination of the other GFCI and the light (I only want to run two cables out to the pole, not three if I can help it).

My plan is to use a common/shared neutral for the two circuits running on the 12/3 wire. One of the hot wires will feed the GFCI with the other feeding the light. I'll split the neutral prior to any connection, with neutrals running separately to the GFCI (LINE side only, the only thing on this circuit) and to the light. Each of the circuits (red and black) will be connected to its own 20amp breaker (single pole, connected right next to each other on separate phases - on the same column of my Siemens Loadcentre panel).

My question is in regards to the breakers. Does anyone know if Alberta code requires that the two circuits with the common neutral be on a two-pole breaker? I would like the capability to turn off the light without dropping power to the GFCI (which would happen if they are permanently tied together). I know it would be a good safety precaution to take in practice (to make sure both circuits are off before anyone works on either of the circuits, considering the common neutral), but I'd be the only one that might need to work on the wiring on this and I'd plan to put a reminder about the shared neutral on the panel anyway.

Could I simply use a tie-bar and take it off for the occasions when I might want just the light off (for the all too rare occassions I get by binoculars or telescope out - need dark skies for that! )?

I could get around it if necessary by adding an outdoor switch before the light, but I'd like to minimize the number of things I tie into the line, and would be fine simply switching off the single breaker controlling the light. If I can't get away from a double pole, I'd obviously need go the route of a switch.